1. Field of the Invention
The present invention relates to a small-sized solid-state laser apparatus, in particular, an optical pickup, an optical printer apparatus, or an exciting light source apparatus, for example, for use in optical measurement, non-linear wavelength conversion, and other applications.
2. Description of the Related Arts
In recent years, high power semiconductor lasers have been made at low cost, and thereby the activities of the research and development and the sales of future merchandise have been spurred in the field of solid-state laser crystals excited by the semiconductor laser.
Regarding such a solid-state laser crystal, since the spectrum width of the exciting light source thereof is very narrow, as compared with that of conventional lamp excitement, the solid-state laser operates very effectively. Furthermore, the size of the semiconductor laser employed as the exciting light source can be made small. Such a solid-state laser crystal is very suitable for being miniaturized and operating with high efficiency. Moreover, such a solid-state laser crystal has a feature that not only can support high power successive oscillation at room-temperature and realize high quality beam, but the solid-state laser crystal is very superior in the energy accumulating property and frequency stability.
Furthermore, in the wave conversion technology utilizing the above-mentioned solid-state laser and the non-linear optical crystal, research and development and the sales thereof have been highly advanced. In particular, the generation of a secondary harmonic wave of the solid-state laser fundamental wave does not damage the preferable beam property of the solid-state laser fundamental beam, and only the wavelength thereof can be converted to the half wavelength. Consequently, such a solid-state laser crystal can be expected to serve in the future as a visible light source such as blue, green, etc. and as an exciting light source for use in an ultraviolet light source realized by generating a fourth harmonic wave of the solid-state laser fundamental wave. Research and development and sales of future products employing such a solid-state laser crystal have been performed actively.
The utilization of laser light sources is widely applied to mechanical processing, measurement, and so on. However, the production of a small-sized and lightweight light source is needed for the light source to be portable, or used in an optical pickup, etc. In order to realize such light sources, the structure of the laser as shown in FIG. 5 is adopted generally.
FIG. 5 is an explanatory diagram for explaining an example of the solid-state laser apparatus described in the published specification of Japanese Laid-open Patent Publication No. 6-152045/1994. In FIG. 5, the reference numeral 1 represents an exciting semiconductor laser, 2 a collimation lens for collimating the semiconductor laser light, 3 a focusing lens for focusing the semiconductor laser light, 4 a laser crystal, 5 a non-linear optical crystal for generating a secondary harmonic wave, and 6 an output mirror.
Dielectric coatings 4a and 4b are formed on both end surfaces of the laser crystal 4. The end surface of the laser crystal at the side of the incident semiconductor laser light is formed such that the reflection coefficient of the end surface at the incident light side is high for the laser fundamental wavelength, also high for the secondary harmonic wavelength, and the transmission coefficient is high for the semiconductor laser light wavelength. At the end surface at the interior side of the resonator, the transmission coefficient is set to a high value for the laser fundamental wavelength and the secondary harmonic wavelength. Dielectric substance coatings are also formed on both end surfaces of the non-linear optical crystal 5 for generating the secondary harmonic wave, such that the transmission coefficients of both end surfaces are respectively set to high values for the laser fundamental wavelength and for the secondary harmonic wavelength.
A dielectric substance coating is formed on the output mirror such that the reflection coefficient thereof is set to a high value for the laser fundamental wavelength and the transmission coefficient thereof is also set to a high value for the secondary harmonic wavelength.
By setting the reflection coefficients on the respective end surfaces as mentioned above, the resonator for the laser fundamental wavelength is constructed between the exciting-side end surface and the output mirror. The non-linear optical crystal for generating the secondary harmonic wave is disposed in the interior thereof. In such a construction, it is possible to generate the secondary harmonic wave with high efficiency by utilizing the high light intensity of the laser fundamental wave in the interior of the resonator.
In the laser apparatus of the construction mentioned above, the parts are respectively separated. Therefore, there exist some problems to be solved in that a holder for the parts is required to be prepared at the time of assembling those parts as the apparatus and the adjustment works have to be done after assembling. Furthermore, there exist some other problems to be solved in that the number of used parts turns out to be large and the cost of manufacturing rises. Those problems obstruct the miniaturization of the apparatus and thereby result in making the apparatus large-sized. Furthermore, it is impossible to provide the apparatus at low cost.
FIGS. 6a and 6b are structural diagrams showing an example of conventional technology shown in published specification of Japanese Laid-open Patent Publication No. 5-211360/1993. The structure thereof is constructed with, as shown in FIG. 6a, an exciting semiconductor laser 21, a semiconductor laser focusing lens 22, a laser crystal 24, a non-linear optical crystal 25 for generating the secondary harmonic wave, and an output mirror 27.
Dielectric coatings are respectively formed on the laser crystal 24, the non-linear optical crystal 25 for generating the secondary harmonic wave, and the output mirror, in the same way as in the case of FIG. 5. The laser apparatus of the above-mentioned structure operates in the same way as that of FIG. 5.
The structure as shown in FIGS. 6a and 6b is realized for the purpose of preventing (or eliminating) the alignment shift of the optical parts of the solid-state laser crystal excited by the semiconductor laser. As shown in FIG. 6b, a groove for holding the optical parts is formed (engraved) on the enclosing rod having a shape of a pair of half-cut cylinders, and the optical parts are inserted therebetween. In such manner, alignment shift can be prevented. Even in such a structure, the number of the parts used cannot be reduced and thereby miniaturization of the apparatus is difficult to achieve.
Furthermore, in the structures of the two examples mentioned above, there exists no selectivity for the laser longitudinal mode. When the output of the semiconductor laser is made large (in the case of strong excitement), the laser longitudinal mode turns out to be a multiple mode and thereby the laser property is lowered (deteriorated). Furthermore, the conversion efficiency to the secondary harmonic wave may become difficult. Consequently, it turns out to adversely effect high efficiency laser operation but the quality of the longitudinal and lateral modes thereof is improved.
For this reason, regarding the conventional small-sized laser light source, there exist some limitations in size, cost, efficiency, etc.
As mentioned heretofore, in the conventional solid-state laser apparatus, the respective parts arc separated from each other. When those parts are assembled to form the apparatus (solid-state laser apparatus), a holder is required to hold the respective parts and adjustment works are needed after assembling those parts.
In addition, there exist some other problems in that the number of parts increases and the cost of manufacturing the device rises. Parts count and cost serve as obstacles to the miniaturization of the apparatus. Therefore, the apparatus inevitably turns out to be large-sized. Moreover, it is impossible to provide the apparatus at low cost.